Process for separating alkylation product, alkylation reaction and separation process, and related apparatus

ABSTRACT

A liquid phase alkylation product from an alkylation reaction unit is introduced into a first heat-exchanger directly or after being pressurized with a pressure pump and heat-exchanged with a vapor phase stream from the column top of a high-pressure fractionating column n, then introduced into a second heat-exchanger and further heated to 100° C.-150° C., then introduced into the high-pressure fractionating column and subjected to fractionation at 2.0 MPa-4.0 MPa, the vapor phase stream from the column top of the high-pressure fractionating column is heat-exchanged with the liquid phase alkylation product to be separated, a liquid phase stream from the column bottom of the high-pressure fractionating column is introduced into a low-pressure fractionating column and subjected to fractionation under at 0.2 MPa-1.0 MPa, a low-carbon alkane is obtained from the column top of the low-pressure fractionating column n, and a liquid phase stream obtained from the column bottom of the low-pressure fractionating column is an alkylation oil product.

The present application is a U.S. national phase entry of InternationalApplication No. PCT/CN2019/104629, filed on Sep. 6, 2019, which claimsthe priority to Chinese patent application 201811039325.5 filed on Sep.6, 2018.

TECHNICAL FIELD

The present invention relates to a process for separating a mixture anda separation apparatus, in particular to a process for separating analkylation product of low-carbon alkene and alkane and a separationapparatus.

BACKGROUND TECHNOLOGY

An alkylation oil is a clean high-octane gasoline blending component.Under the action of a strong acid, an isoalkane (mainly isobutane) andan alkene (C3-05 alkene) react to generate an alkylation oil mainlycomposed of isooctane. Alkylation technology can be divided into liquidacid alkylation and solid acid alkylation according to the catalystform. The alkylation reaction of alkenes and alkanes is verycomplicated, the main reaction is the addition reaction of alkenes andalkanes, but various side reactions also occur at the same time, mainlyincluding the superposition of alkenes, the cracking of macromoleculesand the like. In order to increase the concentration of the reactantisobutane and to suppress the occurrence of side reactions such as thesuperposition of alkenes, it is necessary to maintain a highalkane/alkene ratio in the reaction system. In the sulfuric acidalkylation process currently used in industry, the externalalkane/alkene ratio of the reactor feed is about 7-10, and the internalratio is as high as several hundreds or even thousands; the hydrofluoricacid process also has a large isobutane recycle, with an externalisobutane/alkene ratio of about 5-20, depending on the selected reactorconfiguration; for the solid acid alkylation technique, higher externaland internal ratios are used, and the solid acid alkylation processesdisclosed in U.S. Pat. Nos. 5,986,158 and 7,875,754 require using theexternal ratios of at least 5:1, preferably 16-32:1. The result of usinga higher external ratio is a very low proportion of the alkylation oilin the stream from the reactor outlet: for the liquid acid process, theproportion of the alkylation oil to the inlet of the main fractionatingcolumn is about 10%-30%, and for the solid acid process, that proportionis even lower, typically less than 10%. The large isobutane recycleresults in the high energy consumption in the main fractionating columnn, which is also the most significant cause for the higher energyconsumption in the alkylation process. In the prior art, the energyconsumption of the liquid acid process is about 100 kgEo/ton alkylationoil, and the energy consumption of the solid acid process is as high as200 kgEo/ton alkylation oil. At least 80% of all energy consumption isused in the separation process of the alkylation oil and the recycledisobutane in the product, and the energy consumption is mainly caused bythe fact that the condensation low-temperature heat of a large amount oflow-carbon hydrocarbons cannot be effectively recovered and utilized.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is toprovide a process and an apparatus for separating an alkylation productof low-carbon alkenes and alkanes, which can improve the heatutilization efficiency and remarkably reduce the energy consumption inthe separation process of the alkylation product.

A process for separating an alkylation product, wherein a liquid phasealkylation product from an alkylation reaction unit is introduced into afirst heat-exchanger directly or after being pressurized with a pressurepump and heat-exchanged with a vapor phase stream from the column top ofa high-pressure fractionating column n, then introduced into a secondheat-exchanger and further heated to 100° C.-150° C., then introducedinto the high-pressure fractionating column and subjected tofractionation under a condition of 2.0 MPa-4.0 MPa, the vapor phasestream from the column top of the high-pressure fractionating column isheat-exchanged with the liquid phase alkylation product to be separated,a liquid phase stream from the column bottom of the high-pressurefractionating column is introduced into a low-pressure fractionatingcolumn and subjected to fractionation under a condition of 0.2 MPa-1.0MPa, a low-carbon alkane is obtained from the column top of thelow-pressure fractionating column n, and a liquid phase stream obtainedfrom the column bottom of the low-pressure fractionating column is analkylation oil product, wherein the high-pressure fractionating columnis preferably a flash column n.

An alkylation reaction and separation process comprises: (1) analkylation raw material is contacted with an acidic catalyst in analkylation reaction unit to perform an alkylation reaction, and thematerial after the reaction is discharged as an alkylation product outof the alkylation reaction unit; (2) the liquid phase alkylation productfrom the alkylation reaction unit is introduced into a firstheat-exchanger directly or after being pressurized with a pressure pumpand heat-exchanged with a vapor phase stream from the column top of ahigh-pressure fractionating column n, then introduced into a secondheat-exchanger and further heated to 100° C.-150° C., then introducedinto the high-pressure fractionating column n and subjected tofractionation under a condition of 2.0 MPa-4.0 MPa, the vapor phasestream from the column top of the high-pressure fractionating column isheat-exchanged with the liquid phase alkylation product to be separated,a liquid phase stream from the column n bottom of the high-pressurefractionating column is introduced into a low-pressure fractionatingcolumn and subjected to fractionation under a condition of 0.2 MPa-1.0MPa, a low-carbon alkane is obtained from the column top of thelow-pressure fractionating column n, and a liquid phase stream obtainedfrom the column bottom of the low-pressure fractionating column is analkylation oil product.

An apparatus for separating an alkylation product comprises a pressurepump, a first heat-exchanger, a second heat-exchanger, a high-pressurefractionating column and a low-pressure fractionating column which aresequentially connected in series, wherein an inlet of the pressure pumpis provided with a stream to be separated, an outlet of the pressurepump is communicated with the first heat-exchanger, an outlet of thesecond heat-exchanger is communicated with an inlet of the raw materialfor the high-pressure fractionating column n, an outlet of the columnbottom stream for the high-pressure fractionating column is communicatedwith an inlet of the raw material for the low-pressure fractionatingcolumn n, an outlet of the column top stream for the high-pressurefractionating column is communicated with an inlet of the hotter fluidmedium for the first heat-exchanger, an outlet of the hotter fluidmedium for the first heat-exchanger is communicated with an inlet of thecolumn top reflux for the high-pressure fractionating column n,specially, an outlet of the hotter fluid medium for the firstheat-exchanger, in one part, is communicated with an inlet of the columntop reflux for the high-pressure fractionating column and in the otherpart, returns to an inlet of an alkylation reactor.

The process and the apparatus for separating an alkylation productprovided by the present invention have the following beneficial effects:

(1) Aiming at the characteristics of the large proportion and the lowcondensation potential temperature of the recycled stream in thealkylation product, the potential temperature of the recycled stream isincreased by using a high-pressure flash evaporation method, and theheat is recovered by heat-exchanging with the alkylation product to beseparated, thereby the aims of saving energy and reducing consumptionare fulfilled;

(2) A large part of the recycled stream is firstly separated through ahigh-pressure fractionating column n, so that concentrating thealkylation oil in a low-pressure fractionating column is realized, thetotal amount of the vapor-phase in the fractionating column is reduced,the improvement of the operation reasonability of the low-pressurefractionating column is facilitated, and the structure size of the unitequipment is greatly reduced.

(3) The equipments for the high-pressure fractionation and thelow-pressure fractionation are simple, the operation difficulty issmall, the control is easy, and the energy-saving effect is prominent.

(4) The technical solution of the present invention is particularlysuitable for the separation of the alkylation reaction product obtainedby using a liquid acid catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram for the process for separating analkylation product provided by the present invention.

FIG. 2 is a schematic flow diagram for the process for separating analkylation product used in Comparative Examples 1 and 2.

In said figures: 1—pipeline for the alkylation raw material,2—alkylation reaction unit, 3—pipeline for the alkylation product,4—liquid phase pressure pump, 5—first heat-exchanger, 6—secondheat-exchanger, 7—high-pressure fractionating column n, 12—low-pressurefractionating column n, 8, 9, 10, 11, 13, 14—pipelines.

DETAILED DESCRIPTION OF THE INVENTION

The specific embodiments of the present invention will be described indetail below with reference to the accompanying drawings. It should beunderstood that the specific embodiments described herein are only usedto illustrate and explain the present invention and are not intended tolimit the present invention.

1. DEFINITION

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by those skilled in theart to which this invention belongs. In case of conflict, the presentspecification, including definitions, will control. In the presentinvention, the pressure is expressed as gauge pressure; the operatingpressure of the column is expressed as the column top pressure.

(1) Alkylation Reaction Unit

According to the present invention, the alkylation reaction refers tothat an alkane (e.g. an alkane having 3-5 carbon atoms) is reacted withan alkene (e.g. an alkene having 3-5 carbon atoms) under pressure in thepresence of a catalyst to form an alkane (particularly an isoalkane)having a longer chain, and the alkylation product is present in thestate of liquid phase. In the alkylation reaction unit, a solid orliquid catalyst is used. In the case of a solid catalyst, the alkylationreaction product may exit the alkylation reactor and directly go to asubsequent separating unit. In the case of a liquid catalyst, thealkylation reaction unit further comprises an acid removal operation,and the acid-removed alkylation reaction product exits the alkylationreaction unit and goes to a subsequent separating unit. The alkylationreaction and the acid removal process and the associated apparatuses inthe alkylation reaction unit are known in the art.

(2) Liquid Phase Alkylation Product

According to the present invention, the liquid phase alkylation productcomprises unreacted C3-C5 alkanes (mass fraction: greater than 50%, forexample 50-90%, 50-95%, or 50-99%), a small amount of the remainingalkenes (mass fraction: less than 10%, less than 9%, less than 8%, lessthan 7%, less than 6%, less than 5%, less than 4%, less than 3%, lessthan 2%, less than 1%), and a mixture having a distillation range ofabout 25° C.-about 220° C., especially about 25° C.-about 180° C. as theproduct (mass fraction: 1%-40%). In the case of the solid catalyst, theliquid phase alkylation product can contain 5%-15% of the mixture havinga distillation range of about 25° C.-about 220° C., especially about 25°C.-about 180° C. as the product; and in the case of the liquid catalyst,the liquid phase alkylation product can contain 10%-30% of the mixturehaving a distillation range of about 25° C.-about 220° C., especiallyabout 25° C.-about 180° C. as the product.

(3) Low-Carbon Alkane

In the present invention, the low-carbon alkane refers to C3-C5hydrocarbons with isoalkanes (for example isobutane) as the maincomponent, wherein the content of isoalkanes is higher than 50%, 60% ormore, 70% or more, 80% or more, 90% or more, 95% or more, 96% or more,97% or more, 98% or more, 99% or more, based on the total weight of thelow-carbon alkane, and the low-carbon alkane also comprises other C3-C5alkanes and alkenes.

(4) Alkylation Oil Product

In the present invention, the alkylation oil product refers to a mixturehaving a distillation range of about 25° C.-about 220° C., especiallyabout 25° C.-about 180° C. The alkylation oil product is mainly composedof isoalkanes, which comprise greater than 80%, and has an alkenecontent of less than 2%, and an isooctane content of greater than 50%.

(5) Fractionating Column and Flash Column

In the present invention, the fractionating column comprises a feedinlet, a rectifying section, a stripping section, a column topcondenser, a column bottom reboiler, an optional inter-condenser, and anoptional inter-reboiler.

In the present invention, the flash column refers to such afractionating column n, which does not include the stripping section andthe reboiler of a general fractionating column n, and more particularly,which does not include the stripping section, the column bottomreboiler, the inter-condenser, and the inter-reboiler of a generalfractionating column n, but includes the feed inlet, the rectifyingsection, and the column top condenser of a general fractionating columnn.

(6) Alkylation Raw Material

In the present invention, the alkylation raw material refer to C3-C5alkanes and C3-05 alkenes, wherein the molar ratio of alkane to alkeneis 5-30:1, for example 5-15:1 or 8-20:1.

2. PROCESS FOR SEPARATING AN ALKYLATION PRODUCT

In a basic embodiment of this section, the present invention provides aprocess for separating an alkylation product, wherein said processcomprises: a liquid phase alkylation product from an alkylation reactionunit is introduced into a first heat-exchanger directly or after beingpressurized with a pressure pump and heat-exchanged with a vapor phasestream from the column top of a high-pressure fractionating column n,then introduced into a second heat-exchanger and further heated to 100°C.-150° C., then introduced into the high-pressure fractionating columnand subjected to fractionation under a condition of 2.0 MPa-4.0 MPa, thevapor phase stream from the column top of the high-pressurefractionating column is heat-exchanged with the liquid phase alkylationproduct to be separated, a liquid phase stream from the column bottom ofthe high-pressure fractionating column is introduced into a low-pressurefractionating column and subjected to fractionation under a condition of0.2 MPa-1.0 MPa, and a low-carbon alkane is obtained from the column topof the low-pressure fractionating column n, and a liquid phase streamobtained from the column n bottom of the low-pressure fractionatingcolumn is an alkylation oil product.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the high-pressure fractionating column is aflash column n. In the flash column n, there is provided with a fillerhaving a certain height or column plate(s), a reflux configuration isprovided at the column top, and no reboiler is provided at the columnbottom.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the low-pressure fractionating column is aconventional packed column or a conventional plate column n, a refluxconfiguration is provided at the column top, and a reboiler is providedat the column bottom.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the liquid phase alkylation product to beseparated has a temperature of 0° C.-100° C., more preferably 0° C.-50°C. and a pressure of 0.1 MPa-4.0 MPa, more preferably 0.1 MPa-2.0 MPa.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the high-pressure fractionating column has anoperating temperature of 90° C.-150° C., and a column top reflux ratioof 0.1-2.0.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the high-pressure fractionating column has acolumn top vapor-phase temperature of 90° C.-150° C. or 100° C.-150° C.,a column bottom liquid phase temperature of 90° C.-150° C. or 100°C.-150° C., a column top reflux ratio of 0.1-2.0, a column top recoveryratio of 0.5-0.9 (for example 0.7-0.75), and an operating pressure of0.1 MPa-4.0 MPa (for example 2.0 MPa-4.0 MPa, still further 2.0 MPa-2.8MPa), wherein the column bottom liquid phase temperature is higher thanthe column top vapor-phase temperature.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the low-pressure fractionating column has acolumn top temperature of 30° C.-60° C., a column bottom temperature of100° C.-180° C., and a column top reflux ratio of 0.5-5.0.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the low-pressure fractionating column has acolumn top temperature of 20° C.-80° C. (for example 30° C.-60° C.), acolumn bottom temperature of 100° C.-180° C., a column top reflux ratioof 0.5-5.0 (for example 1), and an operating pressure of 0.2 MPa-1.0 MPa(for example 0.5 MPa-0.6 MPa).

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the temperature difference between the liquidphase alkylation product to be separated and the vapor phase stream fromthe column top of the high-pressure fractionating column is greater than10° C., more preferably greater than 30° C.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the liquid phase alkylation productpressurized by the pump has a pressure of 2.0 MPa-4.0 MPa.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, after being heated by the heat-exchangingwith the first heat-exchanger and the second heat-exchanger, the liquidphase alkylation product has a temperature of 100° C.-150° C., and avapor-phase fraction of 0.3-1.0.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the pressure pump is a liquid phase pump,preferably a pipe-type pump, more preferably a liquid phase centrifugalpump.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the vapor phase stream from the high-pressurefractionating column n, which is heat-exchanged in the firstheat-exchanger, is wholly condensed into the liquid phase, the condensedliquid phase, in one part, returns to the column top of thehigh-pressure fractionating column as reflux, and in the other part,returns to the alkylation reaction unit, the low carbon alkane from thecolumn top of the low-pressure fractionating column returns to thealkylation reaction unit.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the alkylation product to be separated andthe vapor-phase stream from the high-pressure flash column areheat-exchanged in the first heat-exchanger, preferably in the manner ofthe cross-flow heat-exchanging, and the heat-exchanged alkylationproduct to be separated has a temperature of 90-140° C.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, all heat-exchangers are in the manner of thecross-flow heat-exchanging.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the operating pressure of the high-pressurefractionating column is higher than the operating pressure of thelow-pressure fractionating column by 1-3 MPa, for example, 1-2 MPa, forexample greater than 1 MPa and less than 2 MPa.

3. ALKYLATION REACTION AND SEPARATION PROCESS

In a basic embodiment of this section, the present invention provides analkylation reaction and separation process, wherein said processcomprises: (1) an alkylation raw material is contacted with an acidiccatalyst in an alkylation reaction unit to perform an alkylationreaction, and the material after the reaction is discharged as analkylation product out of the alkylation reaction unit; (2) the liquidphase alkylation product from the alkylation reaction unit is introducedinto a first heat-exchanger directly or after being pressurized with apressure pump and heat-exchanged with a vapor phase stream from thecolumn top of a high-pressure fractionating column n, then introducedinto a second heat-exchanger and further heated to 100° C.-150° C., thenintroduced into the high-pressure fractionating column n and subjectedto fractionation under a condition of 2.0 MPa-4.0 MPa, the vapor phasestream from the column top of the high-pressure fractionating column isheat-exchanged with the liquid phase alkylation product to be separated,a liquid phase stream from the column n bottom of the high-pressurefractionating column is introduced into a low-pressure fractionatingcolumn and subjected to fractionation under a condition of 0.2 MPa-1.0MPa, and a low-carbon alkane is obtained from the column top of thelow-pressure fractionating column n, and a liquid phase stream obtainedfrom the column bottom of the low-pressure fractionating column is analkylation oil product.

One or more of the embodiments mentioned in the above Section 2 may beused in any of the embodiments mentioned in Section 3 to form a newtechnical solution. For example, it is preferable that the high-pressurefractionating column is a flash column n.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the alkylation catalyst can be a liquid acidcatalyst or a solid acid catalyst.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, a solid acid catalyst is used in thealkylation reaction unit, and the solid acid catalyst is one or more ofa loaded heteropoly acid catalyst, a loaded or unloaded heteropoly acidsalt catalyst, a loaded or unloaded molecular sieve catalyst, a superacid catalyst, an ion exchange resin and an acid-treated oxide catalyst.The alkylation reaction condition in which the solid acid is used as thecatalyst is: the reaction temperature is 50° C.-100° C., the absolutereaction pressure is 1.0 MPa-6.0 MPa, and the external alkane/alkeneratio is 8-30:1. The temperature of the mixed reaction product to beseparated is 0-100° C.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, a liquid acid catalyst is used in thealkylation reaction unit, and the liquid acid catalyst is selected fromany of sulfuric acid, hydrofluoric acid and an ionic liquid. Thealkylation reaction condition in which the liquid acid is used as thecatalyst is: the reaction temperature is 0° C.-50° C., the absolutereaction pressure is 0.1-1.0 MPa, and the external alkane/alkene ratiois 5-15:1. The temperature of the mixed reaction product to be separatedis 0° C.-50° C.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the mass fraction of the alkylation oilproduct in the alkylation product is 1%-40% (for example 5%-15% or10%-30%), and the remaining components are unreacted low-carbon alkanesand others.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the mixed reaction product to be separated ispressurized through a pressure pump, then successively heat-exchangedthrough the first heat-exchanger and further heated through the secondheat-exchanger, and then introduced into the high-pressure flash columnn. The heated stream that is introduced into the high-pressure flashcolumn has a vapor phase fraction of 0.3-1.0.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the high-pressure flash column has anoperating pressure of 2.0 MPa-4.0 MPa and an operating temperature of100° C.-150° C., and a condensation reflux configuration is provided atthe column top with a reflux ratio of 0.1-2.0. The vapor phase streamfrom the column n top of the high-pressure flash column isheat-exchanged with the mixed reaction product to be separated and iswholly condensed into the liquid phase, so that the recovery andutilization of latent heat is realized. The liquefied stream, in onepart, returns to the column n top of the high-pressure flash column asreflux, and in the other part, directly mixed and heat-exchanged withthe stream to the reactor inlet, thereby greatly increasing the heatutilization and the heat-exchanging efficiency.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the stream from the column bottom of thehigh-pressure flash column is introduced into the low-pressurefractionating column for separating the alkylation oil and the remaininglow-carbon alkanes, wherein it is preferable that the operating pressureof the low-pressure fractionating column is 0.2 MPa-1.0 MPa, the columntop reflux ratio is 0.5-5.0, the column top temperature is 20° C.-80°C., and the column bottom temperature is 100° C.-180° C.

In one embodiment in combination with one or more of the embodimentsmentioned in this section, the streams from the column top of thehigh-pressure flash column and the column n top of the low-pressurefractionating column return to the reactor inlet, and are mixed with thefresh feed, heated-exchanged, and then introduced into the reactor forthe alkylation reaction.

4. APPARATUS FOR SEPARATING AN ALKYLATION PRODUCT

In a basic embodiment of this section, the present invention provides anapparatus for separating an alkylation product, which comprises an(optional) pressure pump, a first heat-exchanger, a secondheat-exchanger, a high-pressure fractionating column and a low-pressurefractionating column n, which are sequentially connected in series,wherein an inlet of the pressure pump is provided with a stream to beseparated, an outlet of the pressure pump is communicated with the firstheat-exchanger, an outlet of the second heat-exchanger is communicatedwith an inlet of the raw material for the high-pressure fractionatingcolumn n, an outlet of the column bottom stream for the high-pressurefractionating column is communicated with an inlet of the raw materialfor the low-pressure fractionating column n, an outlet of the column topstream for the high-pressure fractionating column is communicated withan inlet of the hotter fluid medium for the first heat-exchanger, and anoutlet of the hotter fluid medium for the first heat-exchanger iscommunicated with an inlet of the column top reflux for thehigh-pressure fractionating column n; or the stream to be separated isdirectly introduced into the first heat-exchanger, an outlet of thesecond heat-exchanger is communicated with an inlet of the raw materialfor the high-pressure fractionating column n, an outlet of the columnbottom stream for the high-pressure fractionating column is communicatedwith an inlet of the raw material for the low-pressure fractionatingcolumn n, an outlet of the column top stream for the high-pressurefractionating column is communicated with an inlet of the hotter fluidmedium for the first heat-exchanger, and an outlet of the hotter fluidmedium for the first heat-exchanger is communicated with an inlet of thecolumn top reflux for the high-pressure fractionating column n.

One or more of the embodiments mentioned in the above Section 2 may beused in any of the embodiments mentioned in Section 4 to form a newtechnical solution. For example, it is preferable that the high-pressurefractionating column is a flash column n.

5. ALKYLATION REACTION AND SEPARATION APPARATUS

In a basic embodiment of this section, the present invention provides analkylation reaction and separation apparatus, comprising an alkylationreaction unit and the apparatus for separating an alkylation productmentioned in the above Section 4, wherein an outlet of the alkylationreaction unit is communicated with an inlet of the pressure pump or thefirst heat-exchanger of the apparatus for separating an alkylationproduct, and the alkylation reaction unit is a liquid acid alkylationreaction unit or a solid acid alkylation reaction unit. Preferably, thealkylation reaction unit is a liquid acid alkylation reaction unit.

6. SCHEMATIC TECHNICAL SOLUTION

The process of the present invention is described in detail below withreference to the accompanying drawings. FIG. 1 is a schematic flowdiagram of the alkylation reaction and separation process provided bythe present invention. As shown in FIG. 1, a fresh alkylation rawmaterial 1 is mixed with recycled streams 9 and 13 in a certainproportion, and the resulting mixture is heat-exchanged to thetemperature required by the reaction and then introduced into analkylation reactor 2 to perform the reaction. A stream 3 from thereactor outlet is subjected to the pressure adjustment with a liquidphase pressure pump 4, heat-exchanged with a stream 8 from the columntop of the high-pressure flash column 7 through an interiorheat-exchanger 5, then heated to a certain temperature through anexternal heater 6, introduced into the high-pressure flash column 7, andsubjected to the separation of vapour and liquid phases in the flashcolumn 7. The vapor-phase stream 8 from the column top is heat-exchangedwith the stream 3 from the reactor outlet through the interiorheat-exchanger 5 and wholly condensed into liquid phase. In one part,the condensed liquid phase 9 returns to the reactor inlet and isdirectly mixed with the raw material 1 and the recycled stream 13, theresulting mixture is heat-exchanged and introduced into the reactor 2for the further reaction; and in the other part, the liquid phase 10returns to the top of the high-pressure flash column 7 as reflux inorder to control the content of the alkylation oil in the stream 9recovered from the column top. A stream 11 from the column bottom of thehigh-pressure flash column is introduced into the a low-pressurefractionating column 12 for the separation of the alkylation oil and thelow-carbon alkane, wherein the low-carbon alkane 13 recovered from thecolumn top is recycled, and the alkylation oil 14 from the column bottomexits the apparatus.

7. EXAMPLES

The present invention will be further described below in conjunctionwith specific examples, but the present invention is not limitedthereby.

Comparative Example 1

The schematic flow diagram of Comparative Example 1 is shown in FIG. 2.

In the alkylation reaction unit, C4 alkanes and alkenes were subjectedto the alkylation reaction in the presence of a liquid acid catalyst. Aconcentrated sulfuric acid with a concentration of 96 wt % was used asthe catalyst. An isoalkane in the alkylation raw material was mainlycomposed of isobutane and commercially available from Beijing HuayuanGas Chemical Industry Co., Ltd, and its composition was listed in Table1; and a C4 residue after ether removal, obtained from an MTBE apparatusof Refinery Division, Sinopec Yanshan Petrochemical Co., Ltd., was usedas the alkene raw material, and its composition was listed in Table 1.The alkylation reaction temperature was 5° C., the reaction pressure was0.6 MPa, and the external alkane/alkene ratio was 8:1.

The alkylation product from the outlet of the alkylation reactor had atemperature of 5° C. and a pressure of 0.6 MPa, and was subjected to theacid removal and then directly introduced into the low-pressurefractionating column for the separation of the alkylation oil and the C4stream. The content of the alkylation oil in the stream to be separatedwas 20%, and the rest was the unreacted isobutane and n-butane. Thelow-pressure fractionating column was run at an operating pressure of0.5 MPa, a column top temperature of 47° C., a column bottom temperatureof 145° C., and a reflux ratio of 1.0.

The properties of the feed and the product of the low-pressurefractionating column were shown in Table 2, and the main fractionationenergy consumption comparison was shown in Table 3.

Example 1

Example 1 illustrates the effect of the process for separating analkylation product provided by the present invention.

The reaction and separation flow shown in FIG. 1 was used, thealkylation reaction unit was identical to that in Comparative Example 1,and the stream to be separated, i.e. the alkylation product obtainedfrom the alkylation reactor was identical to that in Comparative Example1.

The system and process for separating the alkylation product describedin the present invention was used, and the specific operating conditionswere as follows: the outlet temperature of the external heater was 145°C., the vapor-phase fraction was 0.5, the high-pressure flash column wasrun at an operating pressure of 2.0 MPa, a column top vapor-phasetemperature of 104° C., a reflux ratio of 0.7, a column top recoveryratio (the ratio of the distillate amount at the column top to the feedamount) of 0.4, and a column n bottom liquid phase temperature of 120°C. The column top vapor-phase was cooled to 23° C. after beingheat-exchanged with the stream from the reactor outlet and condensedinto the whole liquid phase. The stream from the column bottom of thehigh-pressure flash column n was introduced into the low-pressurefractionating column for the separation of the alkylation oil and the C4stream, the column top pressure of the low-pressure fractionating columnwas 0.48 MPa, the column top temperature was 45° C., the column bottomtemperature was 143° C., and the reflux ratio was 1.0.

Comparative Example 2

The schematic flow diagram of Comparative Example 2 is shown in FIG. 2.

In the alkylation reaction unit, C4 alkanes and alkenes were subjectedto the alkylation reaction in the presence of a solid acid catalyst. Thealkylation raw material was identical to that of Comparative Example 1,the used catalyst was a loaded molecular sieve catalyst obtained asfollows: a NaY type molecular sieve (produced by Sinopec CatalystDivision) with an FAU structure was subjected to the sodium-removalmodification on the molecular sieve through the steps ofammonium-exchanging and the like, and then subjected to the loading ofplatinum on the catalyst by an ion-exchanging method, wherein the metalcontent was 0.3 wt %; finally, the obtained platinum-loaded molecularsieve and alumina were uniformly mixed in a ratio of 70:30, and themixture was further dried and calcined to prepare a strip-shapedcatalyst. The alkylation reaction was carried out at a temperature of60° C., a pressure of 3.1 MPa and an external alkane/alkene ratio of25:1. The content of the alkylation oil in the stream from the outlet ofthe alkylation reactor was 5.6% with the remainder being the unreactedisobutane and n-butane.

The stream from the outlet of the alkylation reactor was directlyintroduced into the low-pressure fractionating column for the separationof the alkylation oil and the C4 stream, and the low-pressurefractionating column was run at a column top pressure of 0.6 MPa, acolumn top temperature of 53° C., a column bottom temperature of 159°C., and a reflux ratio of 1.0.

The properties of the feed and the product of the low-pressurefractionating column were shown in Table 2, and the main fractionationenergy consumption comparison was shown in Table 3.

Example 2

Example 2 illustrates the effect of the process for separating analkylation product provided by the present invention.

The reaction and separation flow shown in FIG. 1 was used, thealkylation reaction unit was identical to that in Comparative Example 2,and the stream to be separated, i.e. the alkylation product obtainedfrom the alkylation reactor was identical to that in Comparative Example2.

The process for separating an alkylation product according to thepresent invention was used, the outlet pressure of the alkylationreactor was 3.0 MPa, and the pressure of the high-pressure flash columnwas 2.9 MPa, therefore no pressure pump was necessarily disposed betweenthem. The outlet temperature of the first heat-exchanger was 115° C.,the outlet temperature of the second heat-exchanger was 135° C., thevapor-phase fraction of the stream to be separated was 0.9, thehigh-pressure flash column was run at an operating pressure of 2.9 MPa,a column top vapor-phase temperature of 129° C., a reflux ratio of 0.4,a column top recovery ratio of 0.75, and a column bottom liquid phasetemperature of 134° C. The vapor-phase from the column top of the flashcolumn was cooled to 120° C. after being heat-exchanged with the streamfrom the reactor outlet and condensed into the whole liquid phase. Thestream from the column bottom of the high-pressure flash column wasintroduced into the low-pressure fractionating column for the separationof the alkylation oil and the C4 stream, and the low-pressurefractionating column was operated and controlled under the sameconditions as those in Comparative Example 2.

The properties of the feed and the product of the low-pressurefractionating column were shown in Table 2, and the main fractionationenergy consumption comparison was shown in Table 3.

TABLE 1 Properties of the reaction raw materials Component Mass Fraction(%) Isoalkane Propane 1.7 Isobutane 95.2 n-butane 2.0 Butene 1.1 C4residue after n-butene and iso-butene 0.94 ether removal n-butane 4.96Cis-2-butene 24.57 Trans-2-butene 12.33 Isobutane 57.20

TABLE 2 Properties of the feed and the product of the low-pressurefractionating column Comparative Example Comparative Example ItemExample 1 1 Example 2 2 Content of 20.0 5.6 Feedstock Oil, % Content ofthe oil 20.0 35.4 5.6 13.0 introduced into the column, % D86 ofalkylation oil IBP 25.9 25.1 24.8 24.5 10 56.8 58.5 58.2 60.7 30 99.1100.3 99.8 102.9 50 104.8 105.5 105.2 108.5 70 113.7 114.2 113.9 116.290 126.5 127.3 126.8 135.0 FBP 180.5 180.9 180.7 182.6

TABLE 3 Separation Energy Consumption Comparison Reboiler of HeatConsumption External Fractionating Reduced Steam MJ/t Alkylation OilHeater Column Total Consumption % Comparative Example 1 0 3207 3207 —Example 1 852 839 1691 47.3 Comparative Example 2 0 10196 10196 —Example 2 3490 1666 5156 49.4

1. A process for separating an alkylation product, which ischaracterized in that a liquid phase alkylation product from analkylation reaction unit is introduced into a first heat-exchangerdirectly or after being pressurized with a pressure pump andheat-exchanged with a vapor phase stream from the column top of ahigh-pressure fractionating column n, then introduced into a secondheat-exchanger and further heated to 100° C.-150° C., then introducedinto the high-pressure fractionating column and subjected tofractionation under a condition of 2.0 MPa-4.0 MPa, the vapor phasestream from the column top of the high-pressure fractionating column isheat-exchanged with the liquid phase alkylation product to be separated,a liquid phase stream from the column bottom of the high-pressurefractionating column is introduced into a low-pressure fractionatingcolumn and subjected to fractionation under a condition of 0.2 MPa-1.0MPa, a low-carbon alkane is obtained from the column top of thelow-pressure fractionating column n, and a liquid phase stream obtainedfrom the column bottom of the low-pressure fractionating column is analkylation oil product.
 2. The process for separating an alkylationproduct according to claim 1, which is characterized in that thehigh-pressure fractionating column is a flash column n.
 3. The processfor separating an alkylation product according to claim 1, which ischaracterized in that the liquid phase alkylation product to beseparated has a temperature of 0° C.-100° C. and a pressure of 0.1MPa-4.0 MPa; the high-pressure fractionating column has an operatingtemperature of 90° C.-150° C. and a column top reflux ratio of 0.1-2.0;the low-pressure fractionating column has a column n top temperature of30° C.-60° C., a column bottom temperature of 100° C.-180° C. and acolumn n top reflux ratio of 0.5-5.0; and the temperature differencebetween the liquid phase alkylation product to be separated and thevapor phase stream from the column top of the high-pressurefractionating column is greater than 10° C.
 4. The process forseparating an alkylation product according to claim 1, which ischaracterized in that the liquid phase alkylation product to beseparated has a temperature of 0° C.-50° C. and a pressure of 0.1MPa-2.0 MPa; and the temperature difference between the liquid phasealkylation product to be separated and the vapor phase stream from thecolumn top of the high-pressure fractionating column is greater than 30°C.
 5. The process for separating an alkylation product according toclaim 1, which is characterized in that the liquid phase alkylationproduct pressurized by the pressure pump has a pressure of 2.0 MPa-4.0MPa.
 6. The process for separating an alkylation product according toclaim 1, which is characterized in that the liquid phase alkylationproduct, which is heated by the heat-exchanging with the firstheat-exchanger and the second heat-exchanger, has a temperature of 100°C.-150° C. and an vapor-phase fraction of 0.3-1.0.
 7. The process forseparating an alkylation product according to claim 1, which ischaracterized in that the pressure pump is a liquid phase centrifugalpump.
 8. The process for separating an alkylation product according toclaim 1, which is characterized in that the vapor phase stream from thehigh-pressure fractionating column n, which is heat-exchanged in thefirst heat-exchanger, is wholly condensed as liquid phase, and thecondensed liquid phase, in one part, returns as reflux to the column topof the high-pressure fractionating column n, and in the other part,returns to the alkylation reaction unit, and the low-carbon alkane fromthe low-pressure fractionating column returns to the alkylation reactionunit.
 9. An alkylation reaction and separation process, which ischaracterized in that (1) an alkylation raw material is contacted withan acidic catalyst in an alkylation reaction unit to perform analkylation reaction, and the material after the reaction is dischargedas an alkylation product out of the alkylation reaction unit; (2) theliquid phase alkylation product from the alkylation reaction unit isintroduced into a first heat-exchanger directly or after beingpressurized with a pressure pump and heat-exchanged with a vapor phasestream from the column top of a high-pressure fractionating column n,then introduced into a second heat-exchanger and further heated to 100°C.-150° C., then introduced into the high-pressure fractionating columnand subjected to fractionation under a condition of 2.0 MPa-4.0 MPa, thevapor phase stream from the column top of the high-pressurefractionating column is heat-exchanged with the liquid phase alkylationproduct to be separated, a liquid phase stream from the column bottom ofthe high-pressure fractionating column is introduced into a low-pressurefractionating column and subjected to fractionation under a condition of0.2 MPa-1.0 MPa, a low-carbon alkane is obtained from the column top ofthe low-pressure fractionating column n, and a liquid phase streamobtained from the column bottom of the low-pressure fractionating columnis an alkylation oil product.
 10. The alkylation reaction and separationprocess according to claim 9, which is characterized in that thehigh-pressure fractionating column is a flash column n.
 11. Thealkylation reaction and separation process according to claim 9, whichis characterized in that the alkylation catalyst is a liquid acidcatalyst, which is selected from any of sulfuric acid, hydrofluoric acidand an ionic liquid.
 12. The alkylation reaction and separation processaccording to claim 9, which is characterized in that the alkylationreaction condition comprises: the reaction temperature is 0° C.-50° C.,the absolute reaction pressure is 0.1-1.0 MPa, and the externalalkane/alkene ratio is 5-15:1.
 13. An apparatus for separating analkylation product, which is characterized in that it comprises apressure pump, a first heat-exchanger, a second heat-exchanger, ahigh-pressure fractionating column and a low-pressure fractionatingcolumn which are sequentially connected in series, wherein an inlet ofthe pressure pump is provided with a stream to be separated, an outletof the pressure pump is communicated with the first heat-exchanger, anoutlet of the second heat-exchanger is communicated with an inlet of theraw material for the high-pressure fractionating column n, an outlet ofthe column bottom stream for the high-pressure fractionating column iscommunicated with an inlet of the raw material for the low-pressurefractionating column n, an outlet of the column top stream for thehigh-pressure fractionating column is communicated with an inlet of thehotter fluid medium for the first heat-exchanger, and an outlet of thehotter fluid medium for the first heat-exchanger is communicated with aninlet of the column top reflux for the high-pressure fractionatingcolumn n.
 14. The apparatus for separating an alkylation productaccording to claim 13, which is characterized in that the high-pressurefractionating column is a flash column n.
 15. An alkylation reaction andseparation apparatus, which is characterized in that it comprises analkylation reaction unit and the apparatus for separating an alkylationproduct according to claim 13, wherein an outlet of the alkylationreaction unit is communicated with an inlet of the pressure pump of theapparatus for separating an alkylation product, and the alkylationreaction unit is a liquid acid alkylation reaction unit or a solid acidalkylation reaction unit.